1. Field of the Invention
This invention relates generally to position loop control systems. In particular, this invention relates to a position loop control system for controlling a direct current motor which, in turn, controls the positioning of a projector.
2. Description of the Prior Art
Relative motion of an object along a predetermined path of travel according to a predetermined velocity profile and its positioning at a predetermined relative position has conventionally been controlled by circuitry employing a position potentiometer for indicating the position of the object and a tachometer for measuring the velocity of the object. The tachometer velocity is compared with a desired velocity to control the motion of the object in a closed loop servo system. The final position is, in turn, maintained at the end of the motion of the object by a closed loop servo system in response to the output of the position potentiometer.
U.S. Pat. No. 3,539,897 to Marcel R. Sommeria is the closest known prior art to the subject invention. Disclosed therein is a servo control system which may be utilized in combination with numerical control apparatus for machine tools. The servo control system responds to an input signal comprising a train of pulses, the separation of which is modulated to designate programmed movement of the machine. The servo control system, in turn, controls a servo drive apparatus in response to the frequency of the input pulse train, in addition to controlling the servo drive apparatus in accordance with the instantaneous position and velocity of the driven apparatus so that the lag between actual and programmed positions of the driven apparatus may be reduced with no system instability.
Unfortunately, the aforementioned devices of the prior art ordinarily leave something to be desired, especially from the standpoints of system instability, system accuracy, and complexity in design. Moreover, with respect to the former system accuracy and, hence, the positioning of the apparatus being controlled thereby is somewhat less than that desired in complex servo control systems, while the latter is complex, does not operate in exactly the same manner as the subject invention and contains a combination of elements that is somewhat different from that of the present invention.